U.S. patent number 10,186,602 [Application Number 15/277,777] was granted by the patent office on 2019-01-22 for fin structure of semiconductor device.
This patent grant is currently assigned to Taiwan Semiconductor Manufacturing Company. The grantee listed for this patent is Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Hung-Yao Chen, Yen-Yu Chen, Chi-Yuan Shih, Clement Hsingjen Wann, Ling-Yen Yeh.
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United States Patent |
10,186,602 |
Chen , et al. |
January 22, 2019 |
Fin structure of semiconductor device
Abstract
The disclosure relates to a fin field effect transistor
(FinFET). An exemplary FinFET comprises a substrate comprising a
major surface; a fin structure protruding from the major surface
comprising an upper portion comprising a first semiconductor
material having a first lattice constant, wherein the upper portion
comprises a first substantially vertical portion having a first
width and a second substantially vertical portion having a second
width less than the first width over the first substantially
vertical portion; and a lower portion comprising a second
semiconductor material having a second lattice constant less than
the first lattice constant, wherein a top surface of the lower
portion has a third width less than the first width; and a gate
structure covering the second substantially vertical portion.
Inventors: |
Chen; Yen-Yu (Taipei,
TW), Chen; Hung-Yao (Hsin-Chu, TW), Shih;
Chi-Yuan (Hsin-Chu, TW), Yeh; Ling-Yen (Hsin-Chu,
TW), Wann; Clement Hsingjen (Carmel, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Company, Ltd. |
Hsin-Chu |
N/A |
TW |
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Assignee: |
Taiwan Semiconductor Manufacturing
Company (Hsin-Chu, TW)
|
Family
ID: |
53400979 |
Appl.
No.: |
15/277,777 |
Filed: |
September 27, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170018629 A1 |
Jan 19, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14137725 |
Dec 20, 2013 |
9472652 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
29/7853 (20130101); H01L 29/66795 (20130101); H01L
29/0649 (20130101); H01L 29/1054 (20130101); H01L
21/0228 (20130101); H01L 21/823431 (20130101); H01L
27/0886 (20130101); H01L 21/823481 (20130101); H01L
21/32105 (20130101); H01L 21/76224 (20130101); H01L
29/785 (20130101); H01L 21/823821 (20130101) |
Current International
Class: |
H01L
29/66 (20060101); H01L 29/06 (20060101); H01L
29/10 (20060101); H01L 27/088 (20060101); H01L
21/8234 (20060101); H01L 21/321 (20060101); H01L
21/762 (20060101); H01L 21/02 (20060101); H01L
21/8238 (20060101); H01L 29/78 (20060101) |
Field of
Search: |
;257/401 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102301480 |
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Dec 2011 |
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CN |
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1020050001165 |
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Jan 2005 |
|
KR |
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1020130128298 |
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Nov 2013 |
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KR |
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Primary Examiner: Ahmadi; Mohsen
Assistant Examiner: Reddington; Patricia
Attorney, Agent or Firm: Slater Matsil, LLP
Parent Case Text
CROSS-REFERENCE AND PRIORITY
This application is a divisional of U.S. application Ser. No.
14/137,725, filed on Dec. 20, 2013, entitled "Fin Structure of
Semiconductor Device," which application is hereby incorporated
herein by reference.
Claims
What is claimed is:
1. A method of fabricating a fin field effect transistor,
comprising: forming a semiconductor fin protruding from a major
surface of a substrate, the semiconductor fin comprising a first
semiconductor material having a first lattice constant; forming a
shallow trench isolation (STI) region adjacent the semiconductor
fin; recessing a portion of the semiconductor fin to form a recess,
wherein a remaining portion of the semiconductor fin forms a lower
portion of a fin structure; epitaxially growing a second
semiconductor material in the recess, the second semiconductor
material having a second lattice constant greater the first lattice
constant; after epitaxially growing the second semiconductor
material, recessing a portion of the STI region to expose a portion
of the second semiconductor material; and performing a
high-pressure oxidation (HPO) process to the exposed portion of the
second semiconductor material to form an upper portion of the fin
structure.
2. The method of claim 1 further comprising forming a sacrificial
oxide layer covering the exposed portion of the second
semiconductor material before performing the HPO process to the
exposed portion of the second semiconductor material.
3. The method of claim 2, wherein forming the sacrificial oxide
layer comprises an atomic layer deposition (ALD) process.
4. The method of claim 1, wherein performing the HPO process to the
exposed portion of the second semiconductor material to form an
upper portion of the fin structure comprises performing the HPO
process at a temperature of about 300.degree. C. to about
700.degree. C.
5. The method of claim 1, wherein performing the HPO process to the
exposed portion of the second semiconductor material to form an
upper portion of the fin structure comprises performing the HPO
process at a pressure of about 1 atm to about 25 atm.
6. The method of claim 1, wherein performing the HPO process to the
exposed portion of the second semiconductor material to form an
upper portion of the fin structure comprises using an
oxygen-containing reaction gas.
7. The method of claim 1 further comprising after recessing the
portion of the semiconductor fin to form the recess, performing a
cleaning to remove a native oxide on a surface of the semiconductor
fin exposed in the recess.
8. The method of claim 7, wherein performing the cleaning etches
the STI region and expands the recess.
9. The method of claim 1, wherein the HPO process further forms an
oxide region around the upper portion of the fin structure, and
wherein the method further comprises: removing the oxide region;
and forming a gate structure in direct contact with the upper
portion of the fin structure.
10. A method comprising: forming a first semiconductor material
extending upwards from a semiconductor substrate; forming a first
shallow trench isolation (STI) region and a second STI region on
opposing sides of the first semiconductor material; recessing the
first semiconductor material below a top surface of the first STI
region and a top surface of the second STI region; epitaxially
growing a second semiconductor material on the first semiconductor
material between the first STI region and the second STI region;
recessing the first STI region and the second STI region from at
least a top surface of the second semiconductor material to below
the top surface of second semiconductor material; performing a
high-pressure oxidation (HPO) process on a portion of the second
semiconductor material above the first STI region and the second
STI region, wherein the HPO process forms an oxide region of the
second semiconductor material around an interior region of the
second semiconductor material; and removing the oxide region of the
second semiconductor material to expose the interior region of the
second semiconductor material.
11. The method of claim 10 further comprising: depositing a gate
dielectric over and along sidewalls of the second semiconductor
material; and forming a gate electrode over the gate
dielectric.
12. The method of claim 11, wherein after removing the oxide
region, remaining portions of the second semiconductor material and
the first semiconductor material define a fin structure, wherein
the fin structure comprises: a lower portion having a first width
measured between opposing sidewalls of the lower portion; an upper
portion over the lower portion and having a second width measured
between opposing sidewalls of the upper portion, wherein the second
width is greater than the first width; and a channel region over
the upper portion and having a third width measured between
opposing sidewalls of the channel region, wherein the third width
is less than the second width, and wherein a line perpendicular to
a major surface of the semiconductor substrate extends through the
channel region, the lower portion, and the upper portion.
13. The method of claim 10, wherein removing the oxide region of
the second semiconductor material comprises a wet etching process
or dry etching process.
14. The method of claim 10 further comprising before epitaxially
growing the second semiconductor material on the first
semiconductor material between the first STI region and the second
STI region, etching the first STI region and the second STI region
to increase a distance between the first STI region and the second
STI region over the first semiconductor material.
15. The method of claim 10, wherein the first semiconductor
material has a different lattice constant than the second
semiconductor material.
16. A method comprising: forming shallow trench isolation (STI)
region around a first semiconductor material; etching the first
semiconductor material to define a recess above the first
semiconductor material between sidewalls of the STI region; etching
the STI region to widen the recess, wherein after etching the STI
region, a bottom surface of the recess comprises a material of the
STI region and the first semiconductor material; epitaxially
growing a second semiconductor material in the recess; after
epitaxially growing the second semiconductor material in the
recess, reducing a height of the STI region to expose sidewalls of
the second semiconductor material; oxidizing a first region of the
second semiconductor material without oxidizing a second region of
the second semiconductor material; removing the first region of the
second semiconductor material; and forming a gate structure over
the second region of the second semiconductor material.
17. The method of claim 16, wherein oxidizing the first region of
the second semiconductor material comprises performing a high
pressure oxidation (HPO) process on the second semiconductor
material.
18. The method of claim 17 further comprising before performing the
HPO process, forming a sacrificial oxide over and along sidewalls
of the second semiconductor material using an atomic layer
deposition (ALD) process.
19. The method of claim 17, wherein the HPO process comprises
performing the HPO process at a temperature of about 300.degree. C.
to about 700.degree. C. and at a pressure of about 1 atm to about
25 atm using an oxygen-containing reaction gas.
20. The method of claim 16, wherein etching the STI region
comprises using diluted hydrogen fluoric (DHF) acid to etch the STI
region and remove an oxide of the second semiconductor material.
Description
TECHNICAL FIELD
The disclosure relates to integrated circuit fabrication, and more
particularly to a semiconductor device with a fin structure.
BACKGROUND
As the semiconductor industry has progressed into nanometer
technology process nodes in pursuit of higher device density,
higher performance, and lower costs, challenges from both
fabrication and design issues have resulted in the development of
three-dimensional designs, such as a fin field effect transistor
(FinFET). A typical FinFET is fabricated with a thin vertical "fin"
(or fin structure) extending from a substrate formed by, for
example, etching away a portion of a silicon layer of the
substrate. The channel of the FinFET is formed in this vertical
fin. A gate is provided over (e.g., wrapping) the fin. Having a
gate on both sides of the channel allows gate control of the
channel from both sides. In addition, strained materials in
source/drain (S/D) portions of the FinFET utilizing selectively
grown silicon germanium (SiGe) may be used to enhance carrier
mobility.
However, there are challenges to implementation of such features
and processes in complementary metal-oxide-semiconductor (CMOS)
fabrication. For example, non-uniform composition distribution of a
fin structure causes fluctuation of FinFET characteristics such as
increased leakage current, thereby degrading the device
performance. As the gate length and spacing between devices
decrease, these problems are exacerbated.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is best understood from the following
detailed description when read with the accompanying figures. It is
emphasized that, in accordance with the standard practice in the
industry, various features are not drawn to scale and are used for
illustration purposes only. In fact, the dimensions of the various
features may be arbitrarily increased or reduced for clarity of
discussion.
FIG. 1 is a flowchart illustrating a method of fabricating a
semiconductor device according to various aspects of the present
disclosure;
FIG. 2 shows a top view of a semiconductor device comprising a fin
structure according to various aspects of the present disclosure;
and
FIGS. 3-13 are cross-sectional views of a semiconductor device at
various stages of fabrication according to various embodiment of
the present disclosure.
DESCRIPTION
It is understood that the following disclosure provides many
different embodiments, or examples, for implementing different
features of the disclosure. Specific examples of components and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features may be formed between the first and second
features, such that the first and second features may not be in
direct contact. In addition, the present disclosure may repeat
reference numerals and/or letters in the various examples. This
repetition is for the purpose of simplicity and clarity and does
not in itself dictate a relationship between the various
embodiments and/or configurations discussed.
Referring to FIG. 1, illustrated is a flowchart of a method 100 of
fabricating a semiconductor device according to various aspects of
the present disclosure. The method 100 begins with step 102 in
which a substrate is provided. The method 100 continues with step
104 in which a semiconductor fin is formed protruding from a major
surface of the substrate comprising a first semiconductor material
having a first lattice constant. The method 100 continues with step
106 in which a shallow trench isolation (STI) region is formed
surrounding the semiconductor fin.
The method 100 continues with step 108 in which a portion of the
semiconductor fin is recessed to form a fin recess, whereby a
remaining portion of the semiconductor fin forms a lower portion of
a fin structure. The method 100 continues with step 110 in which a
second semiconductor material is epi-grown filling in the fin
recess having a second lattice constant greater the first lattice
constant. The method 100 continues with step 112 in which a portion
of the STI region is recessed to expose a portion of the second
semiconductor material.
The method 100 continues with step 114 in which a high-pressure
oxidation (HPO) process is performed to the exposed portion of the
second semiconductor material to form an upper portion of the fin
structure. The discussion that follows illustrates embodiments of
semiconductor devices that can be fabricated according to the
method 100 of FIG. 1.
FIG. 2 shows a top view of a semiconductor device 200 comprising a
fin structure 220 according to various aspects of the present
disclosure. FIGS. 3-13 are cross-sectional views of a semiconductor
device 200 taken along the line a-a of FIG. 2 at various stages of
fabrication according to various embodiment of the present
disclosure. As employed in the present disclosure, the term
semiconductor device 200 refers to a fin field effect transistor
(FinFET) and is hereinafter referred to as FinFET 200. The FinFET
200 refers to any fin-based, multi-gate transistor. Other
transistor structures and analogous structures are within the
contemplated scope of the disclosure. The FinFET 200 may be
included in a microprocessor, memory cell, and/or other integrated
circuit (IC).
It is noted that the method of FIG. 1 does not produce a completed
FinFET 200. A completed FinFET 200 may be fabricated using
complementary metal-oxide-semiconductor (CMOS) technology
processing. Accordingly, it is understood that additional processes
may be provided before, during, and after the method 100 of FIG. 1,
and that some other processes may only be briefly described herein.
Also, FIGS. 1 through 13 are simplified for a better understanding
of the concepts of the present disclosure. For example, although
the figures illustrate the FinFET 200, it is understood the IC may
comprise a number of other devices comprising resistors,
capacitors, inductors, fuses, etc.
FIG. 2 illustrates a FinFET 200 fabricated using the steps in FIG.
1. For illustration, the FinFET 200 comprises a fin structure 220
and a gate structure 230 traversing over a channel portion of the
fin structure 220. In some embodiments, the fin structure 220
comprises an upper portion 220u (solid line) and a lower portion
220l (dashed line). For illustration, the FinFET 200 comprises two
fins. In some embodiments, the FinFET 200 may comprise less than or
greater than two fins, for example, one fin or three fins.
As depicted in FIG. 3 and step 102 in FIG. 1, a substrate 202 is
provided. In one embodiment, the substrate 202 comprises a
semiconductor substrate (e.g., Si, SiGe, or SiGeB). In alternative
embodiments, the substrate 202 comprises a silicon-on-insulator
(SOI) structure. The substrate 202 may comprise various doped
regions depending on design requirements (e.g., p-type substrate or
n-type substrate). In some embodiments, the doped regions may be
doped with p-type or n-type dopants. For example, the doped regions
may be doped with p-type dopants, such as boron or BF.sub.2; n-type
dopants, such as phosphorus or arsenic; and/or combinations
thereof. The doped regions may be configured for an n-type FinFET,
or alternatively configured for a p-type FinFET.
In one embodiment, a pad layer 204a and a mask layer 204b are
formed on a top surface 202t of the semiconductor substrate 202.
The pad layer 204a may be a thin film comprising silicon oxide
formed, for example, using a thermal oxidation process. The pad
layer 204a may act as an adhesion layer between the semiconductor
substrate 202 and mask layer 204b. The pad layer 204a may also act
as an etch stop layer for etching the mask layer 204b. In an
embodiment, the mask layer 204b is formed of silicon nitride, for
example, using low-pressure chemical vapor deposition (LPCVD) or
plasma enhanced chemical vapor deposition (PECVD). The mask layer
204b is used as a hard mask during subsequent photolithography
processes. A photo-sensitive layer 206 is formed on the mask layer
204b and is then patterned, forming openings 208 in the
photo-sensitive layer 206.
As depicted in FIG. 4 and step 104 in FIG. 1, the structure in FIG.
4 is produced by forming a semiconductor fin 212 protruding from a
major surface 202s of the substrate 202 comprising a first
semiconductor material having a first lattice constant and hence is
also referred to as first semiconductor material 202 in the present
disclosure.
In some embodiments, the mask layer 204b and pad layer 204a are
etched through openings 208 to expose underlying semiconductor
substrate 202. The exposed semiconductor substrate 202 is then
etched to form trenches 210 with the major surfaces 202s of the
semiconductor substrate 202. Portions of the semiconductor
substrate 202 between trenches 210 form the semiconductor fins 212.
In some embodiments, the trenches 210 may be strips (viewed from in
the top of the FinFET 200) parallel to each other, and closely
spaced with respect to each other. In some embodiments, the
trenches 210 may be continuous and surrounding the semiconductor
fins 212.
In the depicted embodiment, the semiconductor fins 212 protruding
from the substrate major surface 202s comprises two fins. The
photo-sensitive layer 206 is then removed. Next, a cleaning may be
performed to remove a native oxide of the semiconductor substrate
202. The cleaning may be performed using diluted hydrofluoric (DHF)
acid.
Liner oxide (not shown) is then optionally formed in the trenches
210. In an embodiment, liner oxide may be a thermal oxide having a
thickness ranging from about 20 .ANG. to about 500 .ANG.. In some
embodiments, liner oxide may be formed using in-situ steam
generation (ISSG) and the like. The formation of liner oxide rounds
corners of the trenches 210, which reduces the electrical fields,
and hence improves the performance of the resulting integrated
circuit.
As depicted in FIG. 5 and step 106 in FIG. 1, the structure in FIG.
5 is produced by forming a shallow-trench-isolation (STI) region
216 surrounding the semiconductor fin 212. In some embodiments, the
trenches 210 are filled with the dielectric material 214. The
dielectric material 214 may include silicon oxide, and hence is
also referred to as oxide 214 in the present disclosure. In some
embodiments, other dielectric materials, such as silicon nitride,
silicon oxynitride, fluoride-doped silicate glass (FSG), or a low-K
dielectric material, may also be used. In some embodiments, the
oxide 214 may be formed using a high-density-plasma (HDP) CVD
process, using silane (SiH.sub.4) and oxygen (O.sub.2) as reacting
precursors. In other embodiment, the oxide 214 may be formed using
a sub-atmospheric CVD (SACVD) process or high aspect-ratio process
(HARP), wherein process gases may comprise tetraethylorthosilicate
(TEOS) and ozone (O.sub.3). In yet other embodiment, the oxide 214
may be formed using a spin-on-dielectric (SOD) process, such as
hydrogen silsesquioxane (HSQ) or methyl silsesquioxane (MSQ).
A chemical mechanical polish (CMP) is then performed to form the
STI regions 216, followed by the removal of the mask layer 204b and
pad layer 204a. In one embodiment, the mask layer 204b is formed of
silicon nitride, the mask layer 204b may be removed using a wet
process using hot H.sub.3PO.sub.4, while pad layer 204a may be
removed using DHF acid, if formed of silicon oxide.
As depicted in FIGS. 6, 7, and 8, upper portions of the
semiconductor fins 212 are replaced by other semiconductor material
to enhance device performance. The structure in FIG. 6 is produced
by recessing a portion of the semiconductor fin 212 to form a fin
recess 232, whereby a remaining portion of the semiconductor fin
212 forms a lower portion 220l of a fin structure 220 (step 108 in
FIG. 1). In some embodiments, a bottom surface 232s of the fin
recess 232 (i.e., a first top surface 212s of the lower portion
220l) has a first width W.sub.1. Further, the fin recess 232 has
substantially vertical sidewalls.
Using the STI regions 216 as a hard mask, an anisotropic plasma
etching process is performed to recess the semiconductor fins 212
that are unprotected or exposed to form fin recesses 232 between
the neighboring STI regions 216. The remaining portions of the
semiconductor fins 212 between the neighboring STI regions 216 are
hereinafter referred to as the lower portion 220l of the fin
structure 220, protruding from the major surface 202s of the
substrate 202. In some embodiments, the lower portion 220l may
include the first semiconductor material 202 having the first
lattice constant. In some embodiments, the first semiconductor
material 202 comprises Si, SiGe, or SiGeB. In some embodiments, the
etching process may be performed using a chemical selected from
Cl.sub.2, HBr, NF.sub.3, CF.sub.4, and SF.sub.6 as an etching
gas.
Next, a cleaning may be performed using DHF acid to remove a native
oxide of exposed portion of the first semiconductor material 202
(i.e. top surface 212s) and portions of sidewalls of the STI
regions 216, if formed of silicon oxide (shown in FIG. 7). As such,
the fin recess 232 widens from the first width W.sub.1 to a second
width W.sub.2. In some embodiments, the widened fin recess 232 also
has substantially vertical sidewalls.
As depicted in FIG. 8 and step 110 in FIG. 1, the structure in FIG.
8 is produced by epi-growing a second semiconductor material 222
filling in the fin recess 232 having a second lattice constant
greater the first lattice constant. In some embodiments, the second
semiconductor material 222 comprises Ge, SiGe, or SiGeB.
In some embodiments, the second semiconductor material 222
comprises Ge. In the depicted embodiment, the second semiconductor
material 222 such as Ge is selectively grown by an LPCVD process to
fill in the fin recess 232. In one embodiment, the LPCVD process is
performed at a temperature of about 350.degree. C. to 450.degree.
C. and under a pressure of about 10 mTorr to about 100 mTorr, using
GeH.sub.4, GeH.sub.3CH.sub.3, and/or (GeH.sub.3).sub.2CH.sub.2 as
epitaxial gases. Optionally, an anneal process after the growing
process is performed at a temperature of about 550.degree. C. to
750.degree. C. to confine dislocation defects on the interface of
the Si and Ge epitaxial layer.
In some embodiments, the second semiconductor material 222
comprises SiGe or SiGeB. In the depicted embodiment, the second
semiconductor material 222 such as SiGe or SiGeB is selectively
grown by an LPCVD process to fill in the fin recess 232. In one
embodiment, the LPCVD process is performed at a temperature of
about 400.degree. C. to about 800.degree. C. and under a pressure
of about 1 Torr to about 200 Torr, using SiH.sub.2Cl.sub.2,
SiH.sub.4, GeH.sub.4, HCl, B.sub.2H.sub.6, and H.sub.2 as reaction
gases.
After the growing, a planarization such as a CMP is performed, so
that a top surface 222s of the second semiconductor material 222 is
substantially level with a top surface 216s of the STI regions 216.
Further, the second semiconductor material 222 along the
substantially vertical sidewalls of the widened fin recess 232 thus
comprises a first substantially vertical portion 222b (such as
unexposed portion 222b of the second semiconductor material 222
shown in FIG. 9) having the second width W.sub.2.
As depicted in FIG. 9 and step 112 in FIG. 1, the structure in FIG.
9 is produced by recessing a portion of the STI region 216 to
expose a portion 222a of the second semiconductor material 222,
resulting in STI recesses 234, a remaining oxide 214, and an
unexposed portion 222b of the second semiconductor material 222.
The remaining oxide 214 surrounding the fin structure 220 is
hereinafter referred to as an isolation structure 218, wherein a
second top surface 218s of the isolation structure 218 is equal to
or higher than the first top surface 212s. In some embodiments, a
distance D between the first top surface 212s and second top
surface 218s is from about 0 nm to about 5 nm. Further, the
unexposed portion 222b is hereinafter referred to as the first
substantially vertical portion 222b.
In some embodiments, the recessing step may be performed using a
wet etching process, for example, by dipping the substrate 202 in
hydrofluoric acid (HF). In some embodiments, the etching step may
be performed using a dry etching process, for example, the dry
etching process may be performed using CHF.sub.3 or BF.sub.3 as
etching gases.
The process steps up to this point have provided the substrate 202
having the second semiconductor material 222 lying on the lower
portion 220l of the fin structure 220. Conventionally, using an
in-situ stream generation (ISSG) oxidation process, the exposed
portion 222a of the second semiconductor material 222 is oxidized
to form a thinner fin for channel portion of a FinFET. However,
since the ISSG oxidation process is performed at a high temperature
of about 900.degree. C. to about 1100.degree. C., Ge in the second
semiconductor material 222 (e.g., Ge, SiGe, or SiGeB) may diffuse
into the lower portion 220l of the fin structure 220 (e.g., Si).
Non-uniform composition distribution of the fin structure 220 may
cause fluctuation of FinFET characteristics such as increased
leakage current, thereby degrading the device performance.
Accordingly, the processing discussed below with reference to FIG.
11 may form a fin structure with uniform composition distribution.
Problems associated with high leakage current due to non-uniform
composition distribution of the fin structure 220 may be reduced
and/or avoided. Thus, Applicant's method may achieve the desired
device performance characteristics, such as low leakage
current.
As depicted in FIG. 11 and step 114 in FIG. 1, for fabricating a
fin structure with uniform composition distribution, the structure
in FIG. 11 is produced by performing a high-pressure oxidation
(HPO) process 236 to the exposed portion 222a of the second
semiconductor material 222 to form an upper portion 220u of the fin
structure 220.
In some embodiments, an optional sacrificial oxide layer 224 is
first formed covering the exposed portion 222a of the second
semiconductor material 222 and extending over the isolation
structure 218 (shown in FIG. 10). In some embodiments, the
sacrificial oxide layer 224 may be a thin film comprising silicon
oxide formed, for example, using a plasma-enhanced atomic layer
deposition (PEALD) process. In one embodiment, the PEALD process is
performed at a temperature of about 100.degree. C. to about
350.degree. C. and under a pressure of about 1 Torr to about 100
Torr, using C.sub.8H.sub.22N.sub.2Si and O.sub.3 (or O.sub.2) as
reaction gases.
Then, the step of the HPO process 236 to the exposed portion 222a
of the second semiconductor material 222 is performed at a
temperature of about 300.degree. C. to about 700.degree. C. and
under a pressure of about 1 atm to about 25 atm, using O.sub.2 as a
reaction gas. The reaction gas may further comprise H.sub.2,
N.sub.2, or H.sub.2O.
As a result of the oxidation, rather than oxidizing the unexposed
portion 222b of the second semiconductor material 222, an HPO oxide
226 of the second semiconductor material 222 is generated. In the
depicted embodiment, the HPO oxide 226 extends into (i.e., in an
inward direction) the exposed portion 222a of the second
semiconductor material 222 and surrounds the remaining exposed
portion 222f of the second semiconductor material 222.
In some embodiments, the remaining exposed portion 222f comprises a
second substantially vertical portion 222m having a third width
W.sub.3 less than the second width W.sub.2 over the first
substantially vertical portion 222b. In some embodiments, a ratio
of the third width W.sub.3 to the second width W.sub.2 is from
about 0.3 to about 0.5. In some embodiments, the remaining exposed
portion 222f further comprises a first tapered portion 222n between
the first substantially vertical portion 222b and the second
substantially vertical portion 222m. In some embodiments, the
remaining exposed portion 222f further comprises a second tapered
portion 222p over the second substantially vertical portion
222m.
In the depicted embodiment, the remaining exposed portion 222f of
the second semiconductor material 222 and the unexposed portion
222b of the second semiconductor material 222 are combined and also
hereafter referred to as an upper portion 220u of the fin structure
220. As such, the upper portion 220u comprises the second
semiconductor material 222 having the second lattice constant. In
some embodiments, the upper portion 220u comprises source/drain
(S/D) portions and a channel portion between the S/D portions. The
channel portion is used to form channel region of the FinFET
200.
In the depicted embodiment, the upper portion 220u of the fin
structure 220 and the lower portion 220l of the fin structure 220
are combined and also hereinafter referred to as the fin structure
220. In some embodiments, the lower portion 220l comprises the
first semiconductor material 202 having a first lattice constant
less than the second lattice constant, wherein a top surface of the
lower portion 220l has the first width W.sub.1 less than the second
width W.sub.2. In some embodiments, a ratio of the first width
W.sub.1 to the second width W.sub.2 is from about 0.85 to about
0.95.
Subsequently, the structure in FIG. 12 is produced by removing the
HPO oxide 226 to expose the remaining exposed portion 222f of the
second semiconductor material 222. In some embodiments, the
removing step may be performed using a wet etching process, for
example, by dipping the substrate 202 in hydrofluoric acid (HF). In
some embodiments, the removing step may be performed using a dry
etching process, for example, the dry etching process may be
performed using CHF.sub.3 or BF.sub.3 as etching gases.
Then, the structure in FIG. 13 is produced by forming a gate
structure 230 covering the remaining exposed portion 222f
(comprising the second substantially vertical portion 222m, the
first tapered portion 222n, and the second taper portion 222p). In
some embodiment, the gate structure 230 comprises a gate dielectric
230a and a gate electrode 230b over the gate dielectric 230a.
In some embodiments, the gate dielectric 230a may include silicon
oxide, silicon nitride, silicon oxynitride, or high-k dielectrics.
High-k dielectrics comprise metal oxides. Examples of metal oxides
used for high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr,
Sc, Y, Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu and mixtures thereof.
In some embodiments, the gate electrode layer 230b may comprise
poly-silicon. In some alternative embodiments, the gate electrode
layer 230b may include a metal such as Al, Cu, W, Ti, Ta, TiN,
TiAl, TiAlN, TaN, NiSi, CoSi, other conductive materials with a
work function compatible with the substrate material, or
combinations thereof.
As such, using the HPO process 236 to form a fin structure with
uniform composition distribution, problems associated with high
leakage current due to non-uniform composition distribution of the
fin structure may be reduced and/or avoided. Thus, Applicant's
method may achieve the desired device performance characteristics,
such as low leakage current.
It is understood that the FinFET 200 may undergo further CMOS
processes to form various features such as contacts/vias,
interconnect metal layers, dielectric layers, passivation layers,
etc.
In accordance with embodiments, a fin field effect transistor
(FinFET) comprises a substrate comprising a major surface; a fin
structure protruding from the major surface comprising an upper
portion comprising a first semiconductor material having a first
lattice constant, wherein the upper portion comprises a first
substantially vertical portion having a first width and a second
substantially vertical portion having a second width less than the
first width over the first substantially vertical portion; and a
lower portion comprising a second semiconductor material having a
second lattice constant less than the first lattice constant,
wherein a top surface of the lower portion has a third width less
than the first width; and a gate structure covering the second
substantially vertical portion.
In accordance with another embodiments, a fin field effect
transistor (FinFET) comprises a substrate comprising a major
surface; a fin structure protruding from the major surface
comprising an upper portion comprising a first semiconductor
material having a first lattice constant, wherein the upper portion
comprises a first substantially vertical portion having a first
width and a second substantially vertical portion having a second
width less than the first width over the first substantially
vertical portion; and a lower portion comprising a second
semiconductor material having a second lattice constant less than
the first lattice constant, wherein a first top surface of the
lower portion has a third width less than the first width; an
isolation structure surrounding the fin structure, wherein a second
top surface of the isolation structure is higher than the first top
surface; and a gate structure covering the second substantially
vertical portion.
In accordance with another embodiments, a method of fabricating a
fin field effect transistor comprises providing a substrate;
forming a semiconductor fin protruding from a major surface of the
substrate comprising a first semiconductor material having a first
lattice constant; forming a shallow trench isolation (STI) region
surrounding the semiconductor fin; recessing a portion of the
semiconductor fin to form a fin recess, whereby a remaining portion
of the semiconductor fin forms a lower portion of a fin structure;
epi-growing a second semiconductor material filling in the fin
recess having a second lattice constant greater the first lattice
constant; recessing a portion of the STI region to expose a portion
of the second semiconductor material; and performing a
high-pressure oxidation (HPO) process to the exposed portion of the
second semiconductor material to form an upper portion of the fin
structure.
In accordance with an embodiment, a method includes forming a first
semiconductor material extending upwards from a semiconductor
substrate. The method also includes forming a first shallow trench
isolation (STI) region and a second STI region on opposing sides of
the first semiconductor material. The method also includes
recessing the first semiconductor material below a top surface of
the first STI region and a top surface of the second STI region.
The method also includes epitaxially growing a second semiconductor
material on the first semiconductor material between the first STI
region and the second STI region. The method also includes
recessing the first STI region and the second STI region below a
top surface of second semiconductor material. The method also
includes performing a high-pressure oxidation (HPO) process on a
portion of the second semiconductor material above the first STI
region and the second STI region, wherein the HPO process forms an
oxide region of the second semiconductor material around an
interior region of the second semiconductor material. The method
also includes removing the oxide region of the second semiconductor
material to expose the interior region of the second semiconductor
material.
In accordance with an embodiment, a method including: forming
shallow trench isolation (STI) region around a first semiconductor
material, etching the first semiconductor material to define a
recess above the first semiconductor material between sidewalls of
the STI region, and etching the STI region to widen the recess.
After etching the STI region, a bottom surface of the recess
includes a material of the STI region and the first semiconductor
material. The method further includes epitaxially growing a second
semiconductor material in the recess, reducing a height of the STI
region to expose sidewalls of the second semiconductor material,
and oxidizing a first region of the second semiconductor material
without oxidizing a second region of the second semiconductor
material. The method further includes removing the first region of
the second semiconductor material and forming a gate structure over
the second region of the second semiconductor material.
While the disclosure has been described by way of example and in
terms of the preferred embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
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